1. Field of the Invention
The invention relates to 4,4'-diisocyanatophenylbenzylether, a process for the preparation thereof by the reaction of 4,4'-diaminophenylbenzylether with phosgene as well as the use thereof as isocyanate component in the production of polyisocyanate polyaddition products, preferably polyurethane plastics.
2. Description of the Prior Art
The properties of polyurethane plastics, in particular of polyurethane elastomers depend, among other things, essentially on the nature of the polyisocyanate used in the production of the plastics. Particularly high quality polyurethane elastomers are obtained when using 1,5-diisocyanato naphthalene as the diisocyanate component. Casting elastomers based on this diisocyanate, in particular, are distinguished by excellent mechanical properties (see, for example, Becker, Braun, Kunststoff-Handbuch, Volume 7, 2nd Edition, (1983), Carl Hanser Verlag).
1,5-diisocyanato naphthalene has the disadvantage, however, that the basic raw material used for its production, naphthalene is only available in limited amounts. The nitration of naphthalene also inevitably leads to an isomer mixture of nitronaphthalenes from which 1,5-dinitronaphthalene has to be isolated. Purification by distillation of the 1,5-diisocyanato naphthalene obtained from the dinitro compound by hydrogenation and subsequent phosgenation of the resulting diamine gives rise to problems as it has a tendency to sublimate. All of this means that high costs are incurred for 1,5-diisocyanato naphthalene.
The processing of 1,5-diisocyanato naphthalene is often difficult because its melting point and its vapor pressure are relatively high. These properties often prevent 1,5-diisocyanato naphthalene from being reacted directly as a melt. Technically complicated processing methods and protective measures are then required to avoid chemical and health problems.
Consequently, there have been many attempts to find an equivalent replacement for 1,5-diisocyanato naphthalene as diisocyanate component in the production of high quality polyurethane plastics.
Thus, for example, DE-OS No. 31 38 421 and DE-OS No. 31 38 422 describe the production of polyurethane elastomers using 4,4'-diisocyanto-1,2-diphenylethane as diisocyanate component. Although plastics having good mechanical properties can be obtained using this diisocyanate, the production of 4,4'-diisocyanato-1,2-diphenylethane is very inconvenient and expensive and, up until now, has been very difficult to carry out industrially.
Furthermore, numerous attempts to use the relatively inexpensive 4,4-diisocyanato-diphenylmethane instead of 1,5-diisocyanato naphthalene for the production of high quality polyurethane elastomers have been made, but all previous attempts to produce polyurethane elastomers based on this diisocyanate having equivalent mechanical and thermal properties to the polyurethane elastomers based on 1,5-diisocyanato naphthalene have failed.
Accordingly, it was the aim of the present invention to provide a new diisocyanate which is comparable to 1,5-diisocyanato naphthalene with respect to its suitability for the production of high quality polyurethane elastomers and which can be produced economically by simple processes.
This aim could be achieved by 4,4'-diisocyanato phenylbenzylether corresponding to the formula ##STR1## and the process for the production thereof.